Question

I have a simple program that reads data from a PNG into a 2D array. I would like to save that data to a .RAW file so that Raw Studio or Irfanview can view the raw image that my program outputs to my_out.raw. Currently if I just write the raw binary data to the my_out.raw file, neither application can actually read the file, that is view the image. What do I need to do to the program below so that I can see the image?

The code to read the PNG files is:

// MAIN.cpp
#include "pngfilereader.h"
#include <string>
#include <vector>

#include <fstream>

int main (int argc, char *argv[])
{
  PNGFileReader pngfr;
  if (!pngfr.decompress_png_to_raw(std::string("/home/matt6809/Downloads"
    "/City.png"))) {
    std::cout << "File decompression error: " << std::endl;
  } else {
    std::ofstream out;
    out.open("./my_out.raw", std::ios_base::out);
    std::vector<std::vector<unsigned char> > data;
    pngfr.get_image_data(data);
    typedef std::vector<std::vector<unsigned char> >::iterator row_it;
    typedef std::vector<unsigned char>::iterator col_it;

    for(row_it rit= data.begin(); rit != data.end(); ++rit) {
      for(col_it cit = rit->begin(); cit != rit->end(); ++cit) {
        out << (*cit);
      }   
    }   
    out << std::endl;
  }
  return 0;
}


#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <png.h>
#include <iostream>
#include <vector>
#include <string>

class PNGFileReader
{
  public:
    PNGFileReader();
    ~PNGFileReader();
    // Public exposed API:
    bool compress_raw_to_png(uint8_t data, int size);
    bool decompress_png_to_raw(const std::string &path);

    // Getters
    long unsigned int get_image_width();
    long unsigned int get_image_height();
    void get_image_data(std::vector<std::vector<unsigned char> > &data);

  private:
    // Helper functions:
    bool read_png(const std::string &path);
    bool create_png_structs(FILE *fp);
    bool free_data();
    bool alloc_data();

    // Member variables:
    png_structp m_pPNG;
    png_infop m_pPNGInfo;
    png_infop m_pPNGEndInfo;
    png_bytepp m_Data;
    long unsigned int m_ImageWidth;
    long unsigned int m_ImageHeight;

    // Enums
    enum PNGBOOL {NOT_PNG, PNG};
    enum PNGERRORS {ERROR, SUCCESS};
};


#include "pngfilereader.h"
#include <stdexcept>

PNGFileReader::PNGFileReader() :
  m_pPNG(NULL),
  m_pPNGInfo(NULL),
  m_pPNGEndInfo(NULL),
  m_Data(NULL),
  m_ImageWidth(0),
  m_ImageHeight(0)
{
}

PNGFileReader::~PNGFileReader()
{
  for (unsigned long int i = 0; i < m_ImageHeight; ++i) {
    if (m_Data[i]) {
      delete m_Data[i];
      m_Data[i] = NULL;
    }   
  }
  if (m_Data) {
    delete m_Data;
    m_Data = NULL;
  }
}

// Public Exposed API
bool PNGFileReader::compress_raw_to_png(uint8_t m_Data, int size)
{
  return PNGFileReader::SUCCESS;
}

bool PNGFileReader::decompress_png_to_raw(const std::string &path)
{
  return read_png(path);
}

// Getters
long unsigned int PNGFileReader::get_image_width()
{
  return m_ImageWidth;
}

long unsigned int PNGFileReader::get_image_height()
{
  return m_ImageHeight;
}

void PNGFileReader::get_image_data(
  std::vector<std::vector<unsigned char> > &data)
{
  for (unsigned long int i = 0; i < m_ImageHeight; ++i) {
    std::vector<unsigned char> v;
    data.push_back(v);
    for (unsigned long int j = 0; j < m_ImageWidth; ++j) {
      std::vector<unsigned char> *vp = &data[i];
      vp->push_back(m_Data[i][j]);
    } 
  }
}

// Private Methods
bool PNGFileReader::read_png(const std::string &path)
{
  /* 
   * Open up the file to read (path) in binary mode
   * first so that if anything goes wrong with libpng
   * we won't have much to undo
   */
  const char *c_path = path.c_str();
  FILE *fp = fopen(c_path, "rb");
  if (!fp)
    return PNGFileReader::ERROR;

  /*
   * Read the first BYTES_TO_READ bytes from file
   * then determine if it is a png file or 
   * not. If png_sig_cmp == 0 all is okay
   */
  enum {BYTES_TO_READ = 8};
  unsigned char sig[BYTES_TO_READ];
  if (!fread(sig, 1, BYTES_TO_READ, fp)) {
    fclose(fp);
    return PNGFileReader::ERROR;
  }

  bool is_png = !png_sig_cmp(sig, 0, BYTES_TO_READ);
  if (!is_png) {
    fclose(fp);
    return PNGFileReader::ERROR;   
  }

  if (!this->create_png_structs(fp)) {
    fclose(fp);
    return PNGFileReader::ERROR;
  }

  /*
   * For error handling purposes. Set a long pointer
   * back to this function to handle all error related
   * to file IO
   */
  if (setjmp(png_jmpbuf(m_pPNG)))
  {
    png_destroy_read_struct(&m_pPNG, &m_pPNGInfo, &m_pPNGEndInfo);
    fclose(fp);
    return PNGFileReader::ERROR;
  }

  /* 
   * Set up the input code for FILE openend in binary mode,
   * and tell libpng we have already read BYTES_TO_READ btyes from 
   * signature
   */
  png_init_io(m_pPNG, fp);
  png_set_sig_bytes(m_pPNG, BYTES_TO_READ);

  /*
   * Using the lowlevel interface to lib png ...
   */
  png_read_info(m_pPNG, m_pPNGInfo);
  m_ImageHeight = png_get_image_height(m_pPNG, m_pPNGInfo);
  m_ImageWidth = png_get_rowbytes(m_pPNG, m_pPNGInfo);
  this->alloc_data();
  png_read_image(m_pPNG, m_Data);

  png_read_end(m_pPNG, NULL);
  png_destroy_read_struct(&m_pPNG, &m_pPNGInfo, &m_pPNGEndInfo);
  fclose(fp);

  return PNGFileReader::SUCCESS;
}

bool PNGFileReader::create_png_structs(FILE *fp)
{
  /* 
   * Create the pointer to main libpng struct, as well as
   * two info structs to maintain information after, and
   * prior to all operations on png m_Data. Only necessary
   * to release resource after function succeeds.
   */
  m_pPNG = png_create_read_struct(PNG_LIBPNG_VER_STRING, (png_voidp)NULL,
    NULL, NULL);
  if (!m_pPNG)
  {
    fclose(fp);
    return PNGFileReader::ERROR;
  }
  m_pPNGInfo = png_create_info_struct(m_pPNG);
  if (!m_pPNGInfo)
  {
    png_destroy_read_struct(&m_pPNG, (png_infopp)NULL,(png_infopp)NULL);
    fclose(fp);
    return PNGFileReader::ERROR;
  }
  m_pPNGEndInfo = png_create_info_struct(m_pPNG);
  if (!m_pPNGEndInfo)
  {
    png_destroy_read_struct(&m_pPNG, &m_pPNGInfo, (png_infopp)NULL);
    fclose(fp);
    return PNGFileReader::ERROR;
  }
  return PNGFileReader::SUCCESS;
}

bool PNGFileReader::free_data()
{
  if (m_ImageHeight == 0 || m_ImageWidth == 0)
    return PNGFileReader::ERROR;

  for (unsigned long int i = 0; i < m_ImageHeight; ++i) {
    if (m_Data[i]) {
      delete m_Data[i];
      m_Data[i] = NULL;
    }
  }
  if (m_Data) {
    delete m_Data;
    m_Data = NULL;
  }
  return PNGFileReader::SUCCESS;
}

bool PNGFileReader::alloc_data()
{
  if (m_ImageHeight == 0 || m_ImageWidth == 0)
    return PNGFileReader::ERROR;

  if (m_Data != NULL)
    this->free_data();

  m_Data = new png_bytep[m_ImageHeight]();           
  for (unsigned long int i = 0; i < m_ImageHeight; ++i) {
    m_Data[i] = NULL;
  }
  try {
    for (unsigned long int i = 0; i < m_ImageHeight; ++i) {
      m_Data[i] = new png_byte[m_ImageWidth];
    }
  }
  catch (std::bad_alloc e) {
    for (unsigned long int i = 0; i < m_ImageHeight; ++i) {
      if (m_Data[i]) {
        delete m_Data[i];
        m_Data[i] = NULL;
      }
    }
    if (m_Data) {
      delete m_Data;
      m_Data = NULL;
    }
    throw e;
  }

  return PNGFileReader::SUCCESS;
}

Answer 1

A “raw” file that is intended to be used with a camera-image processing program like Raw Studio and Irfraview is not a raw-binary dump of the image-data with no header. Instead the “raw” moniker refers to the fact that the image has a minimal amount of image-processing applied in-camera. For instance, the image-data may still be a single-channel monochrome image from the camera’s bayer-pattern CFA, or no white-balance, color-matrix, etc. has been applied, etc. Either way, the image-data is still formatted in a standard binary image file format complete with a header, data-packing method, etc. Examples include formats such as Adobe’s DNG file format (which is based on TIFF), or proprietary formats from camera manufacturer’s themselves such as Canon’s CR2, Nikon’s NEF, etc.

So if you want these raw-file processing programs to read your “raw” file image data, you’ll have to read-up on the binary data specifications the raw-file formats they support, and then re-format the original PNG image-data correctly.